Euraudio PS1Sc and PS1Snhc assembly instructions
Welcome to the Euraudio PS1Sc and PS1Snhc assembly instructions. The PS1Sc is a symmetrical power supply kit with components, and is part of the Euraudio LDA MIN ultra low distortion audio amplifier DiY kit, but can be used for other amplifiers as well. The PS1Snhc is a symmetrical power supply kit with components, and is part of the Euraudio CTA MIN low distortion audio amplifier DiY kit, but can be used for other amplifiers as well.
Please find the specifications of the PS1S here.
Please find the specifications of the PS1Snh here.
Please read through these instructions before doing anything with the DiY kit.
What the PS1Sc and PS1Snhc DiY kits contain and what they contain not
The PS1Sc and PS1Snhc kits contain the PS1S double-sided, fiberglass-reinforced epoxy PCB (fig. 1) and all the electronic and mechanical components to be mandatorily mounted on it (fig. 2), except the filter capacitors, fuses, and cables/wires.
Note: The PS1Snhc that comes with the CTA MIN kit does not include a heatsink, you will have to buy it yourself; a suitable heatsink is Stonecold RAD-A4463/35 for high current output (2x100 Watts / 4 ohms amplifier), or Stonecold RAD-A4755/50 for moderate current output (2x90 Watts / 6 ohms amplifier).
PS1S
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Sizing the filter capacitors and fuses
The filter capacitors and fuses are not part of the DiY kit, you must size these components according to the power and allowed load impedance (e.g. 4 ohms or 8 ohms) of the amplifier. The amplifier power and load impedance also largely determines the necessary transformer. The exact sizing procedure is not so simple, so I'd rather help with a table containing a few examples below. These examples are valid for class B or class AB amplifiers that have an output signal that can approach the supply rail voltages within 3-5 Volts (such as the Euraudio LDA17).
IMPORTANT: For the Euraudio CTA12 and CTA14(A) amplifiers, refer to their assembly instructions, not this table, for information on transformer, buffer capacitor, and fuse sizing.
The recommended transformer VA value is for heavy duty use, with real musical signals a lower VA rated transformer is often enough.
Do not use capacitors with lower capacitance than shown in the table, if you want to exploit the full amplifier power, because the ripple current specification of smaller capacitors may be inadequate. You may choose higher capacitance value, but that translates to higher amplifier power, so that would call for a higher VA rated transformer or for a lower transformer voltage than that shown in the list. (The power supply rejection ratio of the LDA17 is excellent, so generally it makes no sense to use bigger filter capacitors with this amplifier.)
|
Amplifier power |
Transformer |
Recommended fuse (2 pcs) |
Recomm. filter cap (2 pcs) |
|
2x100 W / 4 ohms |
2x27
VAC, 320 VA |
T6.3A |
15,000uF
/ 50V |
|
2x75
W / 4 ohms |
2x24
VAC, 240 VA |
T6.3A |
12,000uF
/ 50V |
|
2x50
W / 4 ohms |
2x22
VAC, 180 VA |
T5A |
10,000uF
/ 40V |
|
2x120
W / 8 ohms |
2x42
VAC, 400 VA |
T5A |
10,000uF
/ 82V |
|
2x100
W / 8 ohms |
2x37 VAC, 320 VA |
T5A |
8,200uF
/ 82V |
|
2x75
W / 8 ohms |
2x32
VAC, 240 VA |
T4A |
8,200uF
/ 63V |
|
2x50
W / 8 ohms |
2x27
VAC, 180 VA |
T3.15A |
6,800uF
/ 50V |
General assembly advice
What you'll need and is not in the DiY kit
Solder iron, solder wire, wire cutter, suitable cables/wires, Phillips 1 (PH1) screwdriver, Phillips 2 (PH2) screwdriver, heatsink compound, drilling machine, 3.5 mm metal drill bit. A PCB holder jig and/or a model-making vice may come handy. Cable insulation stripper is recommended for cables/thick wires. A solder suction pump and/ or desoldering wick may be needed if you make soldering mistakes.
For the PS1Snhc only: Vice, hammer. Screws, washers and nuts for fixing the heatsink to the L-shape and the L-shape to the PCB.
Soldering
Please click this link, if you need soldering tips.
Where polarity matters
There are electronic components which are polarized, these have to be soldered in the right orientation. The polarity is shown in the PCB with appropriate marking. If you solder any of the polarized components not in the correct orientation, that causes trouble when you power up the circuit; either the circuit will malfunction or even some of the components may be damaged.
Detailed help for assembling
Note: I can't help in troubleshooting assembly faults, I can only resend the whole component set on request.
Drilling the fastening holes
It's practical as a first step to drill the holes in the amplifier chassis that will hold the PCB in place. Put the PCB in its intended place within the amplifier enclosure, mark the 4 holes with a marker pen, and then drill the holes with a 3.5 mm drill bit.
Identifying components
The graphical markings and numbers printed on the PCB make it clear where the components belong and in what orientation. Though basic electronic component knowledge is necessary for identification.
In the PS1S PCB, among the supplied components, only the 2 diodes are polarized.
The 100nF ceramic capacitor is to be soldered into position C98.
Into positions C96, C97, you may optionally mount foil capacitors of about 1uF, the lead spacing is 7.5mm in the PCB. Likewise, into positions C94, C95, you may mount ceramic capacitors of about 100nF. These are meant to lower the high frequency impedance of the power supply. It's not mandatory to use them, so they are not part of the DiY kit. When you select these components, the proper voltage rating must be observed.
Connecting the transformer
The secondaries of the transformer must be soldered to the points marked "AC", "AC" és "COM". For a center tapped-secondary, as shown in the left of the image below. For a transformer with two separate, identical secondaries, as shown in the right of the image below: Solder together the undotted end of one of the secondaries with the dotted end of the other secondary to make the COM.
Due to high current peaks and subsequent I2R heating, the wire cross section must be big enough to carry about 4 times the max. output current of the amplifier on the "COM" connection, and big enough to carry about 2 times the max. output current of the amplifier on the "AC" connections each. For home audio amplifiers, 0.75 mm2 is usually enough for both wires.
Securing the heatsink of the bridge rectifier
PS1Snhc
Drill a 3.5 mm diameter through hole into the heatsink, 15.5 mm from the bottom of it, then trim the burr around the hole.
Take the supplied 38x15x2 mm aluminum piece, and with a vice and a hammer, bend it into L-shape so that one section is 22 mm long and the other is 19 mm long. Drill holes as shown in the next image.
First apply some heatsink compound (thermal grease) to the back of the bridge rectifier (D91). Then fix the bridge rectifier to the heatsink, and to the L-shape on the other side. To do this, use an M3 screw, put a flat washer on both the bridge rectifier surface and the L-shape surface, then a spring lock washer on top of that, and then the nut. Insert the feet of the bridge rectifier into the corresponding holes in the PCB, then secure the whole assembly to the PCB with an M4 screw, serrated washer and nut. Solder the bridge rectifier only at the very end, after all screws have been tightened firmly.
PS1Sc
Drill a 3.5 mm diameter through hole into the heatsink, 12 mm from the bottom of it, as shown in the next image, then trim the burr around the hole.
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First apply some heatsink compound (thermal grease) to the back of the bridge rectifier (D91). Then fix the bridge rectifier to the heatsink with the M3x12 screw supplied, and to the corner bracket on the other side. To do this, put a flat washer on both the bridge rectifier surface and the corner bracket surface, then a spring lock washer on top of that, and then the nut. Insert the feet of the bridge rectifier into the corresponding holes in the PCB, then secure the whole assembly to the PCB with the M4x8 screw, serrated washer and nut. Solder the bridge rectifier only at the very end, after all screws have been tightened firmly.
Connecting the grounding points
There is star-like grounding scheme in the PS1S PCB to prevent hum resulting from ground loops. Of course, if you have created a ground loop somewhere else in your amplifier, then hum may still appear. Points "GND", "PGND", "ZGND" and "SPKGND" are all run to the star point, and they all can be used as ground. Connect the loudspeaker ground to the "SPKGND" point, because it has the thickest PCB trace, allowing it to carry the highest currents.
If you use PS1S with the LDA17mc, LDA17hc, LDA172mc, or LDA172hc amplifier, then the ground points in the LDA17 and LDA172 PCBs are identically marked as "GND", "PGND" and "ZGND".
If you use PS1S with the CTA12 or CTA14(A) amplifier, then the ground points in the CTA12 and CTA14(A) PCBs are identically marked as "GND" and "PGND" (there is no ZGND).
Other high current connections
Besides "COM" and "AC", the supply voltage connections "+VCC", "-VCC" and "SPKGND" also carry high currents. These need thick enough wires that can withstand the maximum amplifier output current. In most cases, wires with 0.75 mm2 cross section are enough.
Connecting the chassis
For protection against electric shock, the metal chassis of the amplifier must be connected to the mains earth ground conductor (or alternatively an equivalently effective protection method against electric shock must be used, which we will not cover here). On amplifiers equipped with protective earthing, it's not recommended to connect the ground of the amplifier to the chassis as well, because hum will develop across the protective earthing conductor. Instead, connect the metal chassis at the same point where the earth ground is connected to the point marked "CHAS" in the PS1S PCB, by soldering the free end of the supplied wire with ring lug to this point. So the effect of this ground loop will be minimized.
DO NOT connect the "CHAS" point to the metal chassis, if the amplifier will be powered off old style fused mains distribution panels that do not feature RCB/RCD (Residual Current Breaker/Residual Current Detector) systems. If in doubt, connect the cathode (K) of D93 to the metal chassis.
More information on earth grounding can be found at this page: Earthing Your Hi-Fi - Tricks and Techniques.